This invention relates to an x-ray system, particularly a system for viewing the internal structure of miniature electrical devices.
Miniature electrical devices are known with external electrical bonds whereby an electrical lead is soldered to the device. These kind of bonds are visually inspected, usually with a magnification device because they are too small to be seen by the naked eye. Typically such bonds may be a few microns in diameter.
More recently such devices have included electrical bonds formed at a planar interface of two electrical components. Such bonds are of course hidden from the naked eye by the face to face contact, and it has been proposed to inspect such bonds using an x-ray inspection device.
The aim of the present invention is to provide an x-ray inspection device which has improvements in design, manufacture and use.
A first aspect of the invention relates to a cabinet for an x-ray inspection system. In general terms the cabinet comprises a frame to provide mechanical support for the system components, and an enclosure to provide protection against mechanical, electrical and radiation hazards.
A known cabinet comprises a skeletal frame to which are attached infill panels, and which is designed to support the x-ray system and associated mechanical and electrical equipment. Lead sheet is applied to the frame to contain radiation, followed by external cladding panels.
A significant problem with this kind of construction is that it is very time consuming and expensive to manufacture and assemble the elements of the frame, and the infill and cladding panels to be attached to the frame. It is also problematic to ensure that the lead shielding fits closely to the frame, and is thus fully effective. An additional problem is that it is very difficult to shield that portion of the frame which protrudes to the exterior to provide an attachment for the external cladding panels. Furthermore, a skeletal frame has spaced frame members which may not be adaptable to a different internal configuration of components, without the use of adapter plates, sub-frames or the like.
According to a first aspect of the present invention, a cabinet for an x-ray system comprises an inner housing having an open mouth and being fully insertable with a clearance in an outer housing having an open mouth, the inner and outer housings having attachment means to secure and space the housings in a predetermined relationship, wherein lead shielding comprises a substantially complete intermediate layer extending between the inner and outer housings, and wherein the open mouth is provided with a lead lined closure.
Such a construction provides a relatively light and inherently stiff cabinet by virtue of the spacing of the inner and outer housings. The intermediate lead shielding is preferably applied to substantially the whole exterior of the inner housing before assembly of the outer housing, and is relatively easy to apply because the prior art frame is absent. Special shielding measures need to be taken in the region of attachments of the inner and outer housings, but these are less of a problem than with the prior cabinet construction, in which the skeletal frame protrudes to the exterior; these attachments may in any event be formed after application of the lead shielding in the inner housing. The cabinet according to this aspect of the invention is significantly less expensive to manufacture and assemble than the prior cabinet.
The cabinet of the invention has the particular virtue that the outer housing, which replaces the prior art external cladding, contributes to the strength and rigidity of the cabinet whilst completely enclosing the lead shielding. Furthermore the outer housing comprises an unitary shell for the lead shielding, and can maintain the shielding in place in the event of, for example, a failure of means attaching the shielding to the inner housing. The shielding is preferably restrained by inwardly protruding bosses of the outer housing. The number of fasteners for the cabinet is substantially reduced over the prior construction because separate infill and cladding panels are not required, and the weight of the cabinet is also substantially reduced.
The inner housing comprises a load bearing enclosure capable of supporting components at any location; such a cabinet is accordingly adaptable to many internal configurations of components, and can be re-used in the case of an alternative configuration without adapter plates and the like.
An x-ray inspection device comprises an x-ray source from which an x-ray beam is emitted, and an image intensifier which receives the beam and causes an image to be formed. An object placed between the source and the intensifier may absorb x-rays, and cause a shadow to appear as the image. By moving the object and intensifier relative to the source, the image may be magnified. A video camera provides real time display of the image on a monitor external to the inspection device.
The object may be placed on a manipulator movable in the X, Y and Z axes, and the intensifier is typically placed on the Z axis in line with the x-ray beam. Such an arrangement permits the object to be moved along the Z axis towards and away from the source, and traversed in the X Y plane. Devices for moving a manipulator in the desired three axes are known.
It would be useful to be able to inspect an object other than along the Z axis, and the present invention provides a compact and relatively simple solution to this requirement.
According to a second aspect of the invention, a movable support of an x-ray inspection device comprises a planar frame, a primary carriage mounted on the frame and movable in the plane of the frame from side to side in a first direction, and drive means to move the carriage with respect to the frame, wherein the carriage is pivotable in said plane about an axis perpendicular to said first direction.
Such an arrangement permits an image intensifier to be mounted on the carriage and be tilted towards a relatively fixed x-ray source as the carriage moves sideways in the frame away from nominal position.
Thus, in the nominal position an x-ray source and an image intensifier are aligned on the Z axis with an object therebetween. By moving the intensifier sideways, and tilting it towards the source, the object may be viewed at an angle, so permitting non-perpendicular inspection at e.g. up to 45xc2x0. The object may also be moved sideways in order that the image of a particular feature is in the centre of the field of view, and the object may be moved towards or away from the intensifier in order to change magnification.
Preferably the carriage is pivotable on both sides of the nominal position so as to permit inspection at xc2x145xc2x0, In a preferred embodiment the primary carriage is itself mounted on a secondary carriage which permits tilting in a plane at right angles to the tilting plane of the primary carriage. This arrangement permits all round viewing of an object
In an alternative embodiment, the carriage is movable linearly, and is tiltable so as to permit inspection at 0-45xc2x0, and a rotary table is provided on the manipulator to support an object. This arrangement also permits all round viewing of an object by rotating the table by up to 360xc2x0 so that the object is in the line of sight of the image intensifier.
The carriages and manipulator are preferably servo controlled to ensure precise alignment. The rotary table, where provided, is also preferably servo controlled in order to ensure a precise angular displacement from the datum position.
In the preferred embodiment the or each carriage is mounted on upper and lower linear bearings extending across the frame, and is driven in a manner which ensures higher relative velocity in one bearing than the other, preferably by toothed belt drive. This arrangement ensures precise pivoting with respect to the nominal (vertical) position, and ensures that the intensifier axis remains centred.
A single motor may provide toothed belt drive to both the upper and lower bearings, the differential velocity being achieved by drive pinions of different diameter. Such an arrangement is elegant and space efficient.
Each carriage is mounted to the linear bearings with one fixed and one sliding connection in order to permit the connections to move apart during tilting movement of the carriage.
The x-ray inspection device according to the invention may be controlled by conventional joystick technology, or separate controls for individual servo motors.
One difficulty with a typical x-ray imaging device is to be able to set or determine the reference distance from x-ray source and the image intensifier to a support for an object to be imaged. The reference distance requires setting in order to compensate, for example, for manufacturing tolerances or ambient temperature effects, and is preferably adapted for periodic re-setting.
According to a third aspect, a method of determining a reference distance from an image intensifier to a support for an object to be imaged comprises the steps of imaging a plurality of pre-defined locations on said support by means of an x-ray beam perpendicular to the plane of the support, shifting the image intensifier in a plane parallel to the plane of the support, re-imaging said pre-defined locations by means of an x-ray beam non-perpendicular to the plane of the support, determining the angle of said beam with respect to said locations, and calculating said reference distance by means of trigonometry.
Such a method gives a highly accurate means of setting the reference distance. The pre-defined locations are preferably discontinuities in the support which can be detected by software imaging techniques. Preferably such locations are defined by a series of recesses, typically through holes in the support.
In a preferred embodiment said through holes are countersunk to the same extent on both sides so that the respective countersinks meet in the middle. Such a through hole can be recognised relatively easily by imaging software since it remains as a symmetric pattern when viewed at an angle. The countersink angle should not be less than the maximum angle of view. In the preferred embodiment the countersink has an included angle of 90xc2x0, and the maximum angle of impinging x-rays is 45xc2x0.
In a preferred embodiment the support comprises a rectangular 1 mm plate having through holes of approximately 0.5 mm adjacent the comers thereof, and countersunk on both sides at 45xc2x0. Perpendicular imaging of such holes also permits the linear traverse of the image intensifier to be related to the distance between such holes, and accordingly to provide compensation for displacement errors in the case that the support is movable in the X-Y plane. Displacement may be controlled by way of lead screw, belt or any other convenient method. Such a movable support is of course useful in order to centre an area of interest within the field of view of the image intensifier. For example, the number of lead screw rotations can be precisely related to the distance between the discontinuities, and thus highly accurate intermediate positioning of the support is obtained.
One further difficulty with a tilting intensifier is that of setting the distance from the intensifier to area of interest on the object. Typically an object has depth, and the area of interest may not lie in the plane of the support. In the case of axial imaging, in which the x-ray beam is perpendicular to the support plate, no difficulty arises; the area of interest can be magnified at will, and remains in the centre of the field of view.
However, in the case of imaging at an angle, the plane of the area of interest becomes important. If the reference datum is the plane of the support but the area of interest lies outside that plane, magnification at an angle will cause the area of interest to move sideways from the centre of the field of view. This is a serious difficulty at high magnification, and may result in disorientation of the operator. In accordance with a fourth aspect, the invention provides for setting the reference distance from the image intensifier to the object plane of interest.
In a preferred embodiment the method of setting the reference distance comprises the steps of imaging the object by means of an x-ray beam perpendicular to the support plane of the object, causing the area of interest to be centred in the field of view, imaging the object at a first angle, re-centring the area of interest in the field of view, imaging the object at a second greater angle, re-centring the area of interest in the field of view, and repeating the steps of imaging at a successively greater angle, and re-centring until the image remains at the centre of the field of view for all angles of the x-ray beam. By use of simple trigonometrical techniques, this iterative procedure can automatically determine a new reference height and thus ensure that during magnification, the area of interest remains in the centre of the field of view. Re-imaging at increasing angular steps minimises the risk that the area of interest will leave the field of view entirely.
In the case of inspection of an object having repeated features, and mounted on a support movable in the X-Y plane, the setting of the reference distance to the area of interest permits rapid traversing of the object to each repeated feature, without the need for enlarging the image, centring the new feature in the field of view, and magnifying the new area of interest on the repeated feature. Repeatability and speed is consequently enhanced whilst maintaining the same reference distance.
According to a fifth aspect of the invention, a method of controlling such a device comprise the steps of viewing a first x-ray image of an object in the device, manipulating said first image virtually to best show an area of interest, and causing said device to move said object with respect to an x-ray source and/or an x-ray image intensifier in a real time to generate a second image corresponding to said area of interest.
The user can thus see a virtual image of the entire object, manipulate that image using software to select an area or view of interest, and cause other software to move the object to most closely correspond to the virtual image by using the X, Y and Z co-ordinates of the virtual image. A portion of the object may thus be viewed at high magnification whilst the virtual image is retained so as to permit the user to have an overview of the direction of view with respect to the entire object.
The virtual and real time image are preferably displayed on the same monitor at the same time, the virtual image being located for example in the upper right hand comer of the monitor screen. The virtual image may be created or recreated by real time imaging of an object. In a preferred embodiment, the virtual image is a frozen real time image created solely for the purpose of manipulation and in order to allow the user to quickly select an area of interest rather than manipulate the object in real time until the desired region is in view. The object may be automatically manipulated in real time in order to generate sufficient data to create the virtual reference image. This may be particularly useful where the object is larger than the image intensifier, so that the image intensifier scans the object to determine the boundary thereof, and subsequently constructs a virtual image of the object for the purposes of manipulation.
In use the real time image may be dragged across the screen, or otherwise manipulated by computer mouse, the apparent manipulation causing the object to be moved in real time so that the real time image moves to the desired screen location. Such object movement is preferably quite fast so that the user does not notice a significant lag between mouse operation and the real time movement of the object which results in movement of the real time image.
Typically the virtual image will be created by software imaging techniques at the start of an inspection routine. Once created, the initial image remains as a navigation aid, and the field of view of the object in real time is represented on the virtual image by e.g. a box surrounding the corresponding portion. The size of this box preferably increases or decreases with magnification of the object, and thus can correspond substantially to the instant field of view. The virtual image may tilt or otherwise change attitude to correspond to the direction of viewing of the object.
In the case where the support for the object is rotatable, the attitude of the real time image of the object with respect to the virtual image will change. Preferably the rotatable support has a reference position at the start of an inspection routine, and an arrow indicates the instant direction of view on the virtual image, for example by pointing at a box defining the field of view. Alternatively the virtual image may rotate in synchronisation with the rotatable table.